Harvesting energy from a vibrating structure, such as a vehicle, has involved mounting piezoelectric (PZT) elements along with a proof mass to provide a vibrating beam. Previous investigators found advantage in providing PZT elements so strain is uniform across the area of each PZT element as the cantilever beam spring vibrates. If some areas generate more current than other areas the current from one area is shunted to the other area and some of the power is dissipated. Thus, investigators have looked for schemes that provide uniform strain with a high value.
It is well known that rectangular cantilever beam springs have more strain at the end near the base and less strain near the proof mass. It is possible to provide more uniform strain in bending by tapering the beam in width or in thickness, as shown in in Marks' Standard Handbook for Mechanical Engineers, Eighth Edition, McGraw Hill, 1978, pages. Various tapers are shown including a parabolic curvature, as shown in FIG. 1, and a linear taper.
A book, Energy Scavenging for Wireless Sensor Networks, by Roundy, et al., Kluwer Academic Publishers, 2004, suggested “varying the width of the beam such that the strain along the length of the beam is the same as the strain at the fixed end, resulting in a larger average strain” to improve power obtained from a piezoelectric mounted on the beam.
However, the amount of power output by such a varying width scheme has still not been particularly high. Thus a better scheme is needed to provide more power output from a vibrating beam, and these improvements are provided in this patent application.